I am unable to use any media keys or click the panel icon to adjust the volume, mute sources or use the previous, next, or play/pause media keys. The only error I can find related to this plugin while launching xfce4-panel in a terminal is "Introspect error on :1.17:/org/mpris/MediaPlayer2: dbus.exceptions.DBusException: org.freedesktop.DBus.Error.NoReply: Did not receive a reply. Possible causes include: the remote application did not send a reply, the message bus security policy blocked the reply, the reply timeout expired, or the network connection was broken.
Executing introspect queue due to error"

I would not expect this to completely freeze this plugin however.